Passenger lists to and from Europe were not routinely kept in the UK; only passenger lists from ports outside Europe were recorded. In a few cases passengers are listed where they joined at an intermediate stop (e.g. Melbourne to Antwerp to London).
The record you mention I believe are records of immigration created by the Antwerp authorities for foreigners residing there. They do often note dates of exit as well for those who moved on to other locales. His full file can be seen on Familysearch and begins here, going on for several pages.
The second page of his file is a statement dated 10 Jun 1908, which indicates that Stan Cancea has left for London some 15 days ago, without intent to return (to Antwerp).
If you go forward to page 641, this is the original documentation of his arrival in Belgium. Summary of relevant information:
- Resident Rue du Printemps, 19, house of Mr Klein
- Name: Stan Cancea
- Born Bailesti, Romania, 20th August 1881
- Father Tencu, born
Bailesti, aged 78
- mother Stephanie Firtulescu, born Bailesti, aged
- legal residence Bailesti, Romania, at the house of his parents
- previous residence London, Welberen? Road, 145, Tott??? (Tottenham?)
- Date of arrival in Belgium - 21 Feb 1908
- Papers - passport No. 4985 dated 28 September 1905, issued by authorities in Craiova, Romania.
Now, this suggests that the stop in Belgium was not his original arrival to the UK - he seems to have been resident in London, came for a short trip to Antwerp, and then returned to London.
The places listed all line up - Băileşti is in Dolj county, Craiova is the capital of that county, so it makes sense that he had to get his passport from there.
We can therefore presume from these documents that he left for the UK sometime after 28 September 1905, when his passport was issued in Romania, and before 21 Feb 1908, when he entered Belgium and was listed as previously residing in London.