Yes, it's true - half a million Colombians live in Venezuela. There are tens of thousands of Arabs, and tens of thousands of Asians. Tens of thousands of Brazilians. In fact, Venezuela is the Latin American country that is home to the most migrants.
Most of those leaving Venezuela today are either migrants returning home - or supporters of the terrorists. The vast majority of Venezuelans are staying in Venezuela - and defending their country against US backed terrorists.
But you said "there are five million Colombian immigrants living and working in Venezuela". Now it's down to 10% of that.
If your first claim was a slip of the pen, that's OK.
Half a million still seems very high, but it's much nearer the mark than the original figure you offered.
Certainly quite a few Colombians did go to Venezuela during the worst years of the FARC violence, and it's credible that a number of them married or made other roots that now compel them to stay. The border people on both sides are pretty identical in culture and language. At one time they formed one nation. The only difference is in poverty; the Colombians are poor, but the Venezuelans are infinitely poorer.
But if they have any kind of a family support network remaining in Colombia, they would be long gone. The border is quite open on the Colombian side. though the Venezuelan paramilitaries do close their side often. When the Venezuelan side is open, there isn't exactly a rush to go in.