Muslims invoke Allah for Help, Allah sends the Angels to help Them

Al-Bukhari wrote in the book of battles (in his Sahih) under "Chapter; Allah's statement,

إِذْ تَسْتَغِيثُونَ رَبَّكُمْ فَاسْتَجَابَ لَكُمْ

In substance, what Muslims are being chastised for is their choice of an option which was laced with timidity, desire to relax, and was a thing of temporal benefit. Contrary to that, the intention made by Allah Ta` ala was based on high determination, great objectives and benefits which were perfect and eternal. Then, in the second verse (8), it was further clarified by saying that there was nothing outside the power and control of Allah Ta` ala. If He had so willed, Muslims would have triumphed over the trading caravan, but He deemed it compatible with the station and majesty of the Messenger of Allah, and his noble Companions ؓ that the confrontation should be against the armed force which should result in their conquest, so that it becomes all too clear that truth is, after all, the truth and that falsehood is, after all, nothing but falsehood.

Noteworthy at this point is the question that Allah Ta` ala is All-Knowing, All-Aware and certainly cognizant of the beginning and the end of everything. What then was the expedient consideration behind this ambiguous promise - that Muslims will overcome anyone of the two groups? It seems possible that He could have pinpointed one group precisely and said that such and such group will be overtaken.