It's less misleading then you might think.
There are cases (enough to not be treated as just some random coincidence; with and without vaccination) where people after Covid had a sever reduction of cognitive abilities that they have problems filling out relatively simple forms. So we can clearly speak of a reduction of IQ.
And while there is a lot of research needed and a lot of open questions and already half a year (or so?) into the pandemic we did know from how we observed COVID affecting the brain that it likely will cause a reduction in cognitive abilities at least in some cases which matches the (very many) observations we had since then.
This also matches what we know from other older studies about other virus infections which have some similarity with covid, e.g. causing Neuroinflammation. So every thing we observe and do know about the underlying mechanics implies that there is very likely a causation. (Through we need more studies for Neuroinflammation.)
So scientist do need to research it more and do need to pin down the exact mechanisms this causes reduction of cognitive abilities in some cases to largely varying degrees and how much of it is a direct and a indirect e.g. psychological effect.
But for everyone else it best to assume that getting COVID might reduce IQ if they are unlucky. Because if you aren't a doctor, scientist or similar but just a random person who got COVID it kind doesn't matter if your IQ gets reduced by COVID directly or indirectly or just correlated due to some other factor you don't know about and in turn can't systematically avoid.