I suspect that there is an element of bargaining with or pressing EU in Czech and Poland's move. China just declared the goal of inoculating 40% its populating by June, then the rest by the end of 2021 or early 2022. There are also lots other countries in the queue for China's vaccine. These countries are at the front of the queue, they were also supportive to China's pushing back the anti-China attack. China's production capacity is far from meeting the requirement to cover all these population. Even considering ramping up the production measures, it would be a full year before the demand and supply reach a balance. Before that time, Czech and Poland may have already got what they ordered through EU.
So I am saying their move is more of pressing EU for more vaccine distributions. It is similar to Erdogan talking about joining SCO while being a member of NATO.
From China's perspective, China is not able to help everybody, who would China prioritize? The one with whom China has a friendly relationship, or the one who just slapped China's face? At best, China may squeeze some volume as a symbolic token, but it won't be large enough to make a difference. The token is because of the saying "伸手不打笑脸人" (don't slap the smiling face).