Another reason I think he fought with the Boers was because not only were the volunteers Polish, but many were American too.
Here is some interesting anecdotes:
In February 1900 a group of fifty Americans arrived to join the Boers.
They had been organized by Irish societies in Massachusetts and Chicago.
To get official recognition from the American Red Cross, they had signed
affidavits that they were going to serve as non-combatants, but although
there were four doctors in the unit, the majority intended to take part in
the fighting. They were unlucky enough to arrive just in time to join the
Brigade (being the Irish Brigade - my words) as it retreated in front of
Roberts's massive advance. As soon as things got really bad some of the
men left for home, but the majority remained in Africa until late in 1900.
The last action in which they fought as a unit was during an unsuccessful
Boer attack at Bergendal in August 1900.
These were not the only Americans to fight for the Boers. Apart from those
who had joined the Irish Brigade, there were others who simply joined their
local commando. After Botha's Natal campaign, John Hassell, an American
who had been fighting with the Vryheid commando, formed a small unit of
American Scouts which was said by the Boers to be the strangest body of men
in the war. Howard Hilegas, a reporter for the New York World, wrote about
a Pennsylvanian, John King, who was working on the mines when the war
started. He and his best friend decided to fight in opposing armies. At
the battle of Spionkop, King the 'Boer', captured his 'British' friend and,
after a brief conversation and a farewell grasp of the hand, shot him dead.
Hilegas records that there were 300 Americans in the Boer army at various
times. The one most valued by the Boers (apart from Colonel Blake) was
Otto von Lossberg from Louisiana. He had received military training in
Germany, where he was born, and commanded the guns under Piet de Wet at
Sannah's Post, a crucial battle of the war.
