Elemental bismuth is not a metal, but a semi-metal.
Solid metals have 2 characteristics that distinguish them from other kinds of substances. The first is the existence of free electrons, which makes them electrically conductive and optically reflective. The second is a crystal structure where each atom has many neighbors, whose consequence is that metals are ductile and malleable.
Already in the 18th century, semi-metals have been distinguished from metals. Semi-metals have only the first property. They have free electrons, but they have a crystal structure where each atom has only few neighbors, whose consequence is that semi-metals are fragile, even when pure (most metals can be made fragile by impurities that disrupt the crystal structure, but they are not fragile when pure).
A typical example of a semi-metal is carbon as graphite. Graphite has free electrons and it is a good electric conductor, but it is easily broken by any attempt to deform it.
Elemental bismuth is similar to graphite. It has free electrons, but like graphite, its crystal structure is made of planes of atoms between which there are relatively large distances, so it is fragile like graphite.
The fact that neither bismuth nor graphite are metals, but only semi-metals, is determined by the fact that they have a much higher electro-negativity than metals. The electro-negativity of bismuth is similar to silicon, germanium and antimony (which are also not metals, Si and Ge are semiconductors, while antimony is a semi-metal), and higher than for any true metals. (Semiconductors differ from semi-metals by not having free electrons when pure and at low temperatures; free electrons are produced in semiconductors by various means, e.g. high temperatures, impurities, light, injection etc.)
So the existence of aromatic rings made of bismuth atoms is much less surprising than the existence of aromatic rings made of truly metallic atoms would be.
Despite the fact that the distinction between metals and semi-metals has already been done for almost 300 years, many modern chemistry manuals fail to distinguish them in a consistent way (or worse, some confuse semi-metals with semiconductors). This is a serious mistake, because in practical applications the distinctions between metals, semi-metals and semiconductors are very important. Many technically important materials are semi-metals, for instance many of the carbides or nitrides of the transitional metals.