How Is It Possible That She Bleed When The Full

How is it possible that she bleed when the full intercourse didn't took place btw us .it was just a push and it felt like pushing against the wall with around 50% erection.noticed blood the next morning .we are 100% sure the penetration didn't took place then why blood??is hymen so sensitive and soft that by just a push it will break ? she was 3-4 days from her periods .
Please help