That is true.
Matha-Tek and Sajdah is the same thing, we Muslims also sometimes say “Mein Matha-tekan ja reha haan” when going to the Masjid to pray.
The Guru’s incorporated the poetry of Muslim saints into the Granth Sahib.
The word Khalsa comes from the Arabic word Khaalis meaning pure.
The Guru Granth Sahib also uses Islamic terms for God such as Rabb, Allah, Rahman, Raheem, Kareem etc.
The Mool Mantra is full of Muslim concepts of Tawheed as opposed to the Hindu trinity/polytheism.
Some Muslims believe that Guru Nanak Dev Ji was a Muslim saint who converted to Islam from Hindu-Brahminism but the later Gurus deviated from his message of Islam because of their political differences with the state.