Well, to be fair, the assumption is coming from reports by Andy Signore and Grace Randolph which claim their sources are asserting this is Spiderverse film.
Now whether or not those scoops turn out to be true or not remains to be seen. At this point we don't have an official, i.e. press release, from the studios, that the film is or isn't a Spiderverse film.
Hollywood Reporter and Variety are great, but just because they don't report something ,doesn't mean they may not have heard talk of a Spiderverse film, and it doesn't mean they have their own sources saying similar things.
Ditto with Deadline and other trades of that level. There's alot of behind scuttlebutt that those trades don't report , though I do think its interesting we haven't heard word of HR and Variety trying to debunk the Maguire , Garfield, Spiderverse stories.
Bottom line, we don't know what's going on behind the scenes either way.