Nope it's not 2 plants, unless the new growth poking out is far from the first one and clearly not attached. In that case it's just that a much smaller seedling was overlooked when potting up the first one, and the 2nd one eventually ends up growing.
Oncidiums are orchids which form clumps of bulbs (sympodial growth, vs the monopodial growth of a Phalaenopsis for instance). The number of new growth you get every year depends on the size of the plant. Once a bulb has matured, it will grow another 1-2 new growths. And once those mature, they do the same. So on a large plant you can easily get a dozen or more new bulbs a year.
Does that help?
__________________ Camille
Completely orchid obsessed and loving every minute of it....