Vandanam means offering prayers. You also offer prayer to the Supreme Lord. So that is also accepted as devotional service. Muslims also, they go to the Mosque and offer prayers to Allah. So practically... And in Buddhism... Lord Buddha is accepted as incarnation of Kṛṣṇa in Śrīmad-Bhāgavatam. So we also, Hindus, we worship Lord Buddha as incarnation of God. There is a very nice verse recited by one great poet, Vaiṣṇava poet. You'll be glad to hear. I'll recite it.
- nindasi yajña-vidher ahaha śruti-jātaṁ
- sadaya-hṛdaya darśita-paśu-ghātam
- keśava dhṛta-buddha-śarīra
- jaya jagadīśa hare jaya jagadīśa hare
The purport of this verse is "O Lord Kṛṣṇa, You have assumed the form of Lord Buddha, taking compassion on the poor animals." Because Lord Buddha's preaching was to stop animal killing. Ahiṁsā, nonviolence. His main objective was to stop animal killing.