Unless DumDum can provide the clip or direct timestamp himself, I'm calling fake and gay on this.
DumDum's post was made at 3:37pm*, in the vod Kirsche posts a tweet at 4:05pm, using this we can do a little math (or use a online calculator) and find out that he posted 28 minutes prior to the tweet being post, this means the statement has to be sometime before 00:35:23, removing the intro of the stream that gives us a window of 27 minutes and 45 seconds for the comment to have been made. I've checked this timespan pretty thoroughly and couldn't find anything, lots of Donation reading, not a single mention of Offkai, and I was checking it while the stream was live too, so It isn't like if could have been edited out.
*These are the times in my timezone, this will of course change depending on where you are in the world, but the math will check out no matter what. And in the off chance I got the math wrong and the comment could have been after 35 minutes, I also checked pretty thoroughly there too.
If DumDum does provide a clip or timestamp, I will formally apologize for calling him a False Flagging Faggot.