Karma, samsara, and moksha are not mentioned in the Vedas proper. Those ideas don't come about until the Upanishads [later vedic literature] and came out of the śramaṇa (mystical/occult) movement.

Buddhism also developed out of the śramaṇa movement but had a different interpretation of the mystical experiences. The Buddhist interpretation is actually the opposite of the Hindu one. Nirvana is the opposite of moksha, rebirth is different from reincarnation, anatman (no-soul) is the opposite of atman (soul), sunyata (emptiness) is the negation of brahman.

Saying that Buddhism is a "Hindu philosophy" is about like saying that atheism is a "Christian philosophy."