Why would it not be investing?
Because you do not "invest" more than a hang reg fee?
One can invest in reading, listening to podcast, looking for trends and making research. So it is not only money that one can consider as an investment. (time=money)
Say you reg a domain 4 months ago for the reg fee, because you saw some value in it, you would not consider that as an investment?
Four months later I see the value you saw before me and i spend "x" amount on it, and buy it from you, then yes that would qualify as investing?
Same goes for drops. Plenty of them go for way much higher amount on bids, that it was actually the asking price of the seller before it was left unrenewed. But that is investing (smart investing) ¿?
I dont really care the tag or name one decides to put on the way one gets or holds on to domains.
Same for any asset, like virtual land or any other NFT. How much Ethereum would you of payed for a Cryptopunk in 2017? or even 6 months back? or on a Bored Ape? CryptoPhunks have been delisted from Opensea and Rareble (now relisted on this last one) because Larba Labs sent a DMCA. Could that add value to that project? Maybe yes, maybe no? Nothing is certain on its initial stages, same as for domains.
In a nutshell, hand reg does not mean the opposite on investment by any means.