Investigators have corroborated the claim, partly by checking the attacker's debit card.
The guide recognised him when his photo appeared in the media.
"It was weird because he was one of the most friendly of the group," he said, adding that he seemed very interested, particularly in ancient Egyptian artefacts, and asked questions about the Sphinx.
No link to IS
Hamahmy was seriously wounded by gunshots after attacking a soldier with two machetes, injuring him in the scalp.
His interrogation was suspended on Tuesday because of his deteriorating condition but before that he told investigators that he had acted alone, not under instructions from IS.
No group has yet claimed responsibility for the attack, although before it Hamahmy tweeted part of a speech by IS's former spokesman Abou Mohammed al-Adnani, who was killed in an airstrike in Syria last August.
He said he had not intended to assault soldiers but to make a symbolic attack on France by damaging objects in the museum.
The interrogation will start again when his health is good enough, sources say.
Apartment near Champs Elysées
Hamahmy, whose father is a retired police officer, was born in Mansoura, in the Nile delta, and worked in United Arab Emirates.
His wife is expecting their second child and living in Saudi Arabia.
His visit to France was prepared well in advance, with a visa request made in October, and he arrived on 26 January, renting an apartment near the Champs Elysées avenue for 1,700 euros a week.