Not every one is the same, for you it was absorbed, for several women I've been with has been different but then theres others that have absorbed it, more often its not absorbed.
Never had anal, have you? Unless you've been distended and lost sphincter muscle tone, it stays inside. In fact, if left in anywhere from 1hr onward, the fluid is usually absorbed into the rectal walls. Experienced this with a husband and wife couple, I had anal with her and he with me. I came in her ass, him inside mine. Nothing came out after and we had waited about 90 minutes before using the bathroom. The semen was totally absorbed. I'll never understand why people jump up after anal sex to eject from their body a lover's fluid that belongs inside.