硬 here means 'rigidly / against the odds' (not 'hard' as a texture). 硬是 emphasizes that an action happened/didn't happen contrary to circumstances, expectations, or pressure. Common in colloquial speech across regions.
mistakes
Don't confuse with 还是 (háishi, 'still'). 硬是 carries a 'against resistance / against expectation' nuance that 还是 lacks.
