येऽप्यन्यदेवता भक्ता यजन्ते श्रद्धयाऽन्विताः। तेऽपि मामेव कौन्तेय यजन्त्यविधिपूर्वकम् ॥

ye ’pyanya-devatā-bhaktā yajante śhraddhayānvitāḥ te ’pi mām eva kaunteya yajantyavidhi-pūrvakam

Even the devotees of other Shining Ones, who worship full of faith, they also worship Me, O son of Kuntî, though contrary to the ancient rule.

In plain words: Krishna says that people who worship other gods (the "Shining Ones") with real faith are actually worshipping him too. They are just not doing it in the proper, direct way. Arjuna is called "son of Kunti" after his mother.