Gosh yes, I've seen that floating around after the account was already shut down on twitter. Terrible. 
As far as I know, MangaMaterials' artist is female, though! Just a heads-up, I've seen that correction flying around in a detailed twitter thread, as well. ^^
Apart from that, I will never understand how people can be so insecure that they need to harass an artist off a platform just because they feel called out for their skills being called "beginner". I mean... short brush strokes are a beginner's thing, that's like... fact? Seems like some touchy tumblr kids migrated over to twitter to ruin everything. >_>