No, you didn't, that is pretty much the way to interpret it assuming that we have both an official blogpost entry and Cerny's talk mentioning top-100 titles playable at launch, and the blog mentioning expanding coverage over time. The other interpretation, that he is only referring to boosted titles, and that it requires a few assumptions such as:
1. Talk of a Boost mode that wasn't explicitly stated
2. Why use the wording playable at launch together with top-100 titles if all or most games will be available?
3. Why talk of expanding coverage over time
4. And, perhaps most egregious of all, if all PS4 games work on PS5 day-1 through the use of a different mode, why on earth not state it explicitly in either the talk or the blogpost?
I dunno, Sony might have made a mess of the whole thing, but my feeling is simply that their wording is simply trying to give a positive spin to an aspect that they know is undercooked wrt their main rival.