It's difficult to maintain form over a season, inexperience (including the manager, not a proven winner like Klopp), lack of squad depth, luck, etc. They have won almost every game they have dominated, that's being a bit lucky, given the nature of football. It's likely they will have games in which they hit the post 2-3 times and draw (like us at Southampton last season).
Every team in PL history that won 48+ pts after 19 games did worse in the 2nd half of the season, including the very best versions of City, Liverpool and United. It's not a coincidence. The Centurions dropped only 2 pts in the 1st half of the season and 12 pts in the 2nd half. Liverpool dropped only 2 pts in the first 28 games in 19/20 and 13 pts in the last 10 games, United dropped 8 pts in 3 of the final 5 games in 11/12.
Plus, as good as Ramsdale, Saliba, Saka and Martinelli have been, they ain't prime Alisson, VVD, Mane and Salah, and it will show.
Plus, teams will adjust their tactics against Arsenal. They haven't treated them sufficiently seriously at times and have played more attacking formations than against City. Plus some decsions will go against them. They were a bit lucky vs Liverpool, at 1:1 Liverpool could/should have been awarded a pen, etc.
There are many reasons to think Arsenal won't find it easy over the next 19 games. Several good teams lost form in the 2nd half of a season, not only Newcastle (12 pts clear in 95/96) but even experienced winners like Ferguson's United (97/98 and 11/12).
Nothing is guaranteed, but I think Arsenal don't have the quality and depth to win 90+ pts. Might be wrong, time will tell, etc.