No, owning the majority shares of all companies in the industry does not count as a monopoly because a monopoly market structure consists of a single firm selling a unique product. If the companies whose shares have been purchased are selling homogeneous product then they will be regarded as perfectly competitive industry and if the product is heterogeneous so it the case of imperfect competition. If the companies are merged or they form a cartel then only they will be regarded as a monopoly.