Liverpool points in the Premier League are currently has very difficult to catch by Arsenal, even with the remaining matches, of course, Arsenal chances are very slim especially so far their performance has been very inconsistent after losing many of their front players, especially now that Liverpool have been eliminated from the Champions League, the Premier League will automatically become their main focus this season, as well as Arsenal who no longer have hopes in the Premier League and other domestic trophies will of course focus entirely on the Champions League at this time as said by Arteta after the match against Manchester United.
UCL is just another excuse by Arteta. When you compare his club to the Liverpool, it's totally different. His club is still far away from winning UCL, meanwhile Liverpool is a few steps closer to PL title. He's also walked out after the journalist asked him about PL title challenge against Liverpool.
That's why he said that to avoid being blamed or mocked by his rival. The better you wait until his club leave from UCL, then see what's gonna happen with him.