First, the legislation shrinks the size of the federal district to include a small portion of D.C. where representatives from other states conduct federal business. The Constitution doesn’t say you can’t shrink the federal district; it only says it can’t be larger than “ten miles square” (100 square miles, in modern English). The District has been shrunk before without any changes to the U.S. Constitution, notably when the District ceded much of its southwestern portion to Virginia in the 1840s.
Secondly, the legislation would introduce the residential land currently in the District of Columbia into the United States as the 51st state. Again, states have joined the union without constitutional amendments as recently as 1959 (see: Alaska, Hawaii).