The Gunners had a good opening half against the Cherries where Declan Rice opened the scoring. However, they could not double their advantage.
The Cherries were better following the interval and scored twice in the half through Dean Huijsen and Evanilson in a short sequence.
Speaking after the game, Odegaard said that the second half is not acceptable and the result is a massive disappointment for Arsenal.
He said: "Massive disappointment. I think we started the game pretty well - we got the goal and felt like we controlled pretty much everything.
"But they score and we lose control of the game. We never find the rhythm after that, it is too chaotic and too sloppy from us. The second half is not acceptable."
Arsenal remain on 67 points after 35 games into the season. They are still not guaranteed Champions League football for next campaign.
The club may need at least one more win to secure a berth.