Is Star-Lord indirectly responsible for Tony Stark's death?

No not at all. If anyone would be then it would be Tony himself.

Remember when Star-Lord attacked Thanos both Tony and Spider-man were pulling on the glove trying to get it off of Thanos' hand. It was then that Tony chose to stop helping Spider-Man try to calm Star-Lord down. While he was doing that Spider-man got the glove away from Thanos for a split second. IF Tony had stayed at his post they may have permanently gotten the glove from Thanos.

It is clear to me that Star-Lord's attack distracted Thanos enough for the glove to be removed.

The idea that Star-Lord's actions caused the problem is based on the presumption that the group would have gotten the glove anyway. Nothing indicates this would have happened. The closest they got was AFTER Star-Lord attacked Thanos.