so, this is one of those advices that can be ok, or go wrong.
Let me explain.
Scenario 1: you are trying to save money and start of in community college. You do knock out almost all the prereqs in community college (i would still recommend to take Organic Chemistry and Biochem in university). You get very good GPA, Then you transfer to a university to a science major (chemistry, engineering, or biology). You end up taking a lot of advanced science classes in biology and chemistry because of it. your GPA maybe drops a bit, but you keep it up above 3.5 (or, 3.7 even better). in this scenario you will be ok. No one will care if you took basic biology in community college BECAUSE YOU HAVE UPPER LEVEL TOUGH CLASSES in university. (I did it this way, and trust me, they really dont care).
Scenario 2: you take prereqs in community college, get good GPA, but transferr into a non science major: this is bad. Community college classes are easy compared to university (i took both, so trust me). When the AdCom sees your transcripts, they wont be convinced that you can handle tough science courses on university level... and you HAVE to show them that, because medical school is even tougher. If you cannot handle university science courses, how can they know that you can handle medical school?