Please keep in mind when we are talking about Bajwa, we should see the case of Justice Qazi Isa and his wife as a benchmark. Government saw something fishy, they have filed the reference and now his wife is facing court kacheri to prove how they have purchase property abroad.
Different process and different situation.
Issa is a sitting Supreme Court judge. The Constitutional process allows for a Presidential reference to be submitted and the Supreme Judicial Council (SJC) to take notice and conduct hearings/investigations. Issa challenged that in court and the SC ruled that the issue should not go in front of the SJC and instead directed the FBR to investigate the assets of Issa and his wife.
Should NAB take notice of this?
They could, but the only thing they can ask is whether the $19,000 USD investment by Bajwa's wife can be justified. Given that Bajwa retired as a Lt. General, $19,000 is not a huge amount. They could also question him on any of his other declared assets but we've seen that list (after he became SAPM) and nothing stands out as being 'assets beyond means'.
The rest of the company (prior to Bajwa's wifes investment) was set up by his brothers in the US and the investments obtained were via loans. Bajwa or his wife did not invest or claim to invest any more than the &19K amount. His brothers are based in the US and live and work there so not sure if NAB can question them or what authority it would even have over them.
Honestly, given that I run a business myself and have taken loans in the same manner as Bajwa's brothers, this is pointless and a witch hunt by Army bashers and anti-PTI elements. Bajwa's brothers were doctors and executives. Given how much they earned even before the business, they would have had no issues with getting bank loans using their assets and incomes as collateral.
If the franchises they purchased were existing franchises, the structures and equipment itself would have been used as part of the collateral for the loans they obtained.
In general, running restaurants in the US successfully is extremely hard work - this is not a preferred stop for money laundering given the risks involved. Real estate, stocks etc are a much better investment for illegally obtained money.