@Himechu ... Hum... That was the point ?
Its quite literally stated that the fact they are mother and son is a insiders SECRET, no one is meant to know both of them are mother and son, specially because if we go by logic it can bring backlash whit the company being accused of favoritism and bias, also bringing drama to Uki because she would be labeled as someone who only got her job trough connections, this is proven further as she is literally presented as a semi-famous cooking "YouTuber" who has never been near a TV camera her whole life, which right off the bath seems odd as apart from her connection to cooking, she could be out numbered popularity wise by any bigshot host, but gets easely covered as her just being a "growing" personality similar to Waki.
We also do gets hints to the fact that they do know each other:
1. They went drinking together despite the producers having a massive "Keep away from Drama" policy, which Waki has avoided since the start till meeting MC and basically later having a meltdown on TV to express his love for him, so him going to drink whit a female co-worker would be out of character unless they already knew each other.
2. Despite them being portraid as strangers, we see during the bus scene that Uki is EXTREMELY over-familiar, literally asking Waki "who is kami-san", whit no formality whatsoever, quite literally shoving herself in his private life, you also see Waki get nervous at the question, which would be a weird thing to do after proclaiming your love for "Kami-san" on live TV for everyone to see a few days or weeks ago, kind of hinting Uki is someone who Waki has to hide the fact he has a lover to, we also see Uki addressing Waki by just "You" before taking the pic of the Bento while smiling, overall she shows to not only be over-familiar for someone he doesn't know, but she also shows no ill-intention from the start wen sharing the pic, as its later revealed she fallows the account of our MC.
These 2 points above are enough hints for me to see that her being his mother does make sense, but if you don't think so we can agree to disagree.
But its clear she was used for the jealousy drama plot and later will be used for the meet your parents drama plot.
In a way, if this was the authors actual intentions (which I believe they were), its a smart move of the author since this way we get some consistent characters instead of having 1-off characters just for drama, which is something the author seems to like doing, as he also re-uses the BFF guy from Vol.1 from "the rival" to "the councilor" for Waki and his ark and even this vol. uses the "Homophobic" co-worker as the "Actually likes you" guy, so its clear that the author likes to use characters as more then a "1 trope bloke".