Vaheguru Ji Ka Khalsa, Vaheguru Ji Ke Fateh!
When sikhs matha tek (bow) to Sri Guru Satguru Granth Sahib Ji we are not bowing to the physical but the spirtual essences within it.
Ik Oangkar Satigur Parsaadi
mehalaa 4
"bwxI gurU gurU hY bwxI ivic bwxI AMimRqu swry ]
baanee guroo guroo hai baanee vich baanee anmrith saarae |
The Word, the Bani is Guru, and Guru is the Bani. Within the Bani, the Ambrosial Nectar is contained"
- Sri Guru Satguru Raam Daas Ji, Ang 982
From your question i believe you think that sikh are somewhat idol worshipping, but we are not all we are doing is submitting ourselves to the guru. I also presume that you think a guru should be within a human form for it too look "normal" to bow down, but within the reality of sikhi and life itself our guru is formless, our guru can take anyform, any shape, any size and any colour which our guru has and that is within Sri Guru Satguru Granth Sahib Ji.
I hope i have not made any mistakes within responding to your question, if i have i pray to guru and the panth to forgive me as i am a manmukh is wishing to seek the guru love.
Vaheguru Ji ka Khalsa, Vaheguru Ji Ke Fateh!