What would it mean if a professor of interest (POI) emails me after April 15th asking if I decided where to go for my PhD yet?
Seems to me like you did the right thing. They may really have been impressed by your qualification; or they just wanted to gauge your interest in remaining on the waitlist, to which you replied &quot;yes&quot;.
There's little else we can guess the person might have wanted to ask. You didn't burn any bridges and expressed interest. There's little else anyone could have done in your place.