This is the relevant definition of board:
3 [treated as sing. or pl.] the decision-making body of an organization.
It seems unlikely that these two mean the same thing:
Welcome to the decision-making body of the organization
Welcome to the organization.
Perhaps the problem is the meaning of 'decision-making body'. A decision-making body is usually a smaller group within the organization. Here is a discussion of its use in one context: decision making body