Need advice on dealing with a backseat DM without ruining everyone’s fun

I’m running a DnD adventure for a group of 5. Myself and four of the players are new and one player has been playing for 8+ years. We are running the Storm-wreck Isles starter kit and I did change some aspects but not too many. This player decided to make a Goliath and play him an an intimidating fashion. He said he goes to shake this kolbods hand who’s a friendly NPC and then says he’s rolling intimidation. I said why would that happen if you’re just shaking hands? He says it’s cause his intent is to intimate the small creature. I reluctancy say go ahead and thankfully he rolled low. He did that because Kolbolds are apparently timid “evil” creatures. But in my setting especially here at Dragons Rest in the starter kit this isn’t the case. He’s not interested in the npcs or anything. Even so because he’s being the face of the party he keeps the pace moving faster than I’d like and he’s just trying to rush through the dialogues and assumes everything. Problem is that he’s not wrong all the time. Many times he remembered a rule more accurately than me but other times he’s filling in gaps and calling for rolls. A few times he checked with me but many times he didn’t. It really took the fun of what I thought being a dm was about. Which is to me being a game master, a pace setter, and adeptly the world I built for the party’s play-style. This first experience was extremely mixed. Everyone including him said they had fun but I’m not sure I did. There were a few highlights that were great but the player that did those was the opposite of the veteran player. I awarded her an inspiration point. The group would split if he or I stopped playing and when I try to establish that I’m the person who needs to make roll calls he would bring up how and why it should be this or that. Is it normal for your table to ask for ability checks? I’m very confused on what to do and how to change things for the next session