I just don't think this 100.000 figure, which would almost double the labour force of Wroclaw, is plausible.
"In 2015, the Wroclaw District Employment Agency alone received 36 thousand applications from employers (99% of which concerned Ukrainian nationals) who sought to employ foreign professionals using the simplified procedure. The procedure applies to the citizens of the following six countries: Armenia, Belarus., Georgia, Moldova, Russia and Ukraine, who are legally eligible to work in Poland for 6 months over a period of 12 consecutive months without the necessity to obtain a work permit," says Maciej Sałdacz, Deputy Marketing Head at the District Labour Office in Wroclaw."
So the 100,000 figure is not completely implausible due to the uptick in Ukrainian migration over the past few years. Also more plausible if the "District Labor Office" in Wrocław covers a larger area than just the city itself. And very plausible if it covers the whole województwo.
That's 100,000 Ukrainians working in the city during the course of the year, not at any one time. By far the bulk are temporary or seasonal laborers who work six months out of the year or less, as they are allowed to. I suspect that many of them are provided room and board outside of the city by their employers, and driven to the work site every day. A lot of the rest live in workers' hostels. There was one where I lived in Wrocław and I think most of the residents there were Ukrainians.
This does not translate to 100,000 immigrants, or 100,000 potential home buyers, or as you note, 100,000 happy Biedronka shoppers. And certainly not 100,000 Ukrainians who call Wrocław home.
They also keep to themselves and do not mingle. They don't have the time for that, and they are focused on earning and saving money to take back home in a short time.