Which President Bush? There were two of them. You've tagged it with the second one, so going with that. It's not clear from your teacher's statement which though. So keep in mind the possibility that this was in reference to the first one.
The economy goes into recession regularly. 2008, 2001, 1992, 1982-3, etc. So he may simply have been saying that the economy was going to crash some time.
If the economic crash had started in 2009 rather than 2008 (or 2007 if you prefer), then it would have been perceived as McCain's problem more than Bush's. I say McCain because there is some reason to believe that John McCain would have won if the economy had been better. So if your teacher was pro-McCain, he may have felt that Bush was an idiot for not keeping up appearances for another year or two until he was out of office.
Note that that recession was exceptionally persistent (and likely started early) due to the simultaneous housing crisis. It's not evident that there was much Bush could have done to prevent that.
In general, it is considered better politically for a recession to start early in one's term so that improvement can occur prior to the election. That way the election takes place in the glow of the improvement rather than the darkness of the recession. Outside of one's term is even better, but considering the frequency with which they happen is difficult. Note that Bill Clinton's presidency was bracketed by recessions. So he got credit for the first recovery and skipped out on the blame for the .net crash and recession.