Sikh votes are crucial in maybe 15 out of total 545 seats. To top it of, Modi's BJP is in alliance with Shiromani Akali Dal, the largest and most influential Sikh political party who also happen to have control of the all Sikh religious bodies. Not to forget, the stigma of anti Sikh riots of 1984, fanned and fuelled by the congressi goons. Just a few days ago, two rioters were sentenced to death after all these years. More convictions are to follow. Point being, Siddhu's theatrics are inconsequential as far as the national politics and Modi goes.
The Indian government was always going to announce the Kartarpur Sahid corridor and it was scheduled to coincide with Guru Nanak's 550th Jayanti. Siddhu must have gotten a whiff of it, and pulled the stunt in Imran Khan's inauguration ceremony to try and get credit for it.
Siddhu is an ambitious man and is merely setting himself up as the top contender of Punjab state Congress once Captain Amrinder Singh decides to step down (Which I don't see happening anytime soon). I don't know if you know, but Siddhu was part of the BJP prior to this. Once he realised that he would never get to be the top dog in Punjab, as BJP is a junior partner in the Akali Dal- BJP alliance in Punjab, he quit the BJP and joined Congress. He is as much a hawk now as he was during his days with BJP, so don't let his stunts fool you.