This can be easily ascribed to "just talk" or "cheap talk" from Russia. It's also not the first time that such words have through from Moscow on the matter. Flashback to 2019
Many in the West anticipated the resurgence of a possible alliance between Russia and North Korea on the eve of the first summit between V. Putin and Kim Jong Un, held in Vladivostok in late April 2019. A Kremlin eager to jump into the Korean conundrum, to impede the US strategy of "maximum pressure" and to display its influence and pretence as a great power seemed a predestined scenario. Yet what happened was instead a modest encounter: a few hours of talks without substantial or unexpected announcement.
It is no real surprise that the summit was more in symbolism than in substance, as many observers noticed. Short of a military or economic assistance that Moscow could hardly promise given its obligations under the UNSC sanctions regime that it helped shape, there is little that Russia could do to help Pyongyang in the current circumstances - a modest humanitarian assistance was announced, but only in the aftermath of the summit. Furthermore, Moscow is a marginal economic partner for North Korea – except perhaps in its hosting of thousands of migrant workers (in contrast, China covers 90% of North Korean trade). [...]
The same goes for the negotiation methodology. Moscow has aligned with Beijing on the demand of a resumption of direct negotiations between Washington and Pyongyang; a step by step approach of the denuclearization process; a relaxation of sanctions, and broader security supervision through the Six-Party framework (though Beijing favours a Four-Party format: both Koreas, China and the US). Besides, Moscow supports Chinese expectations of a US military withdrawal from South Korea – and ideally North-East Asia - in the context of a possible peace settlement. [...]
The notion of “security guarantees” also came out of the Vladivostok summit, before the Russian Foreign Minister Lavrov raised it to the press. Accordingly, Russia and China would be ready to “provide security” to North Korea in the framework of a peace settlement. This also illustrates Moscow’s alignment with Beijing. Seen from a Russian perspective, the idea clearly departs from the current situation where Russia and the DPRK are bound by the 2000 “Treaty of Friendship, Good-Neighborliness and Cooperation,” which excludes military assistance. Furthermore, the notion of “security guarantees” that could be jointly provided by China and Russia has little chance to be deemed attractive by a North Korean leadership that is so focused on national independence and self-reliance. Pyongyang would hardly like to trade the burden of American threat with the political cost of any Russian and Chinese security umbrella - especially since it now possesses the nuclear deterrent.
As you can see, as much as Russia tries to be relevant in this matter, it doesn't have a lot of cards to play, except perhaps its UNSC position, and neither China nor the US care much to involve Russia other than nominally. Nor is it likely that Russia can provide terribly credible guarantees to Pyongyang...
Furthermore (same source) the “security guarantees” lingo actually comes form the DPRK's side demands. But it's unclear what it means in practice. It's been speculated that Pyongyang wants nothing short of US withdrawal from the peninsula, something that Russia is rather unlikely to be able to guarantee.
As further discussed in a Carnegie Center analysis, Russia is chiefly intersted in
preserving the status quo in the peninsula. Neither a strengthening of China's position,
e.g. by the coming to power in the DPRK of a more pro-Chinese government, nor some kind of
[truly] democratic reunification of Korea, seen as advancing US interests, is favored in
Moscow. So, that helps explain why Russia is fairly happy to echo whatever vague demands
the current regime in Pyongyang puts out. (A similar analysis about a decade ago [from the Director of Korean Programs of the Russian Academy of Science] came to the same conclusion: that Russia's best bet and true objective is simply the preservation of the Kim regime and just "manage the [nuclear] risk" that comes along with that.)